LONDON, UK - British Prime Minister Theresa May was facing off European leaders on Wednesday in a bid to hammer out a deal for the UK's exit from the European Union.

The biggest stumbling block remains what to do about the Ireland and Northern Ireland border.

Many parts of a settlement have been agreed however there are critical aspects that the parties are finding it difficult to find common ground on.

Prime Minister May was scheduled to make a pitch to the 27 European leaders, on Wednesday after which they would break for dinner, and private discussions.

Months of negotiations between the parties have failed so far to get Britain to a point where it will be able to finalise a deal prior to its exit in March 2019.

EU Council President Donald Tusk is warning European leaders they may need to prepare for a 'no-deal Brexit,' which would see the UK leave the European Union with no formal agreement on areas of trade and cross-border entry in place.

â€‹EU leaders are considering a summit next month at which a final plan could be put to a vote, but they firstly need a draft agreement, which at present is not in the offing.

Whether a deal is negotiated or not, the EU has said it wants Northern Ireland, to remain in the bloc's customs union - to avoid having to implement border controls between Northern Ireland and Ireland.

Ireland, for its part supports the inclusion of Northern Ireland in the bloc, however Britain says it is reluctant to treat Northern Ireland differently to the rest of Britain.

The EU proposal 'threatens the integrity of our United Kingdom,' she told the House of Commons on Monday.